# Young's Modulus Lab Problem

1. Apr 10, 2010

### zooted

1. The problem statement, all variables and given/known data
My graph doesn't look like a typical stress vs strain plot.

[PLAIN]http://dl.dropbox.com/u/2344149/graph.png [Broken]
* y-intercept set to zero and last 4 data points were ignored

Wire diameter= 1.16 mm
L0= 100.2 cm
$$\overline{}L$$'0= 0.015
Young's modulus for steel (actual)= 1.92E11

[PLAIN]http://dl.dropbox.com/u/2344149/data.png [Broken]

2. Relevant equations
Elongation
$$\Delta$$Li=$$\overline{}L$$i-$$\overline{}L$$'0
Strain
$$\Delta$$Li/L0 (converted L0 into mm)
Stress
mg/pi*r2 (radius converted from mm to m and each load is 1 kg)

3. The attempt at a solution
Strain values are very small and stress are very large which is supposed to be correct. The percent error is over 70% An error made during the lab was that the initial length of the wire was measured incorrectly and the mistake was not noticed until the wire had already been stretched. So the we used the final length for our calculations, which would be correct as long as the elastic limit was not exceeded. If it had been permanently deformed I don't think that it would produce such a large error, would it? We also measured the diameter of the wire at the beginning, not after the 5th load like the manual recommends.